Dryopteris cristata, a lowland plant of wet bogs and alder swamp forests, has become a rare and threatened species in south-western Central Europe. In Europe the Alps form the southern border of the distribution area of this nordic-subarctic fern species. The historic distribution and former population sizes of D. cristata in Switzerland and Liechtenstein were reconstructed based on extensive herbarium and literature studies. Present distribution and population sizes were determined in a field survey in which the actual existence of 14 (38% of all described) populations was confirmed. Twenty-two populations are now extinct mainly due to habitat destruction till 1945, resulting in a broad distribution gap between the remaining sites in the western and the eastern parts of the study area. For eleven of the present populations a classification of the former population sizes and their changes was possible. Five of the remaining populations suffered a bottleneck situation with a population size of less than 25 individuals at least once during the last 120 years. At present, three of the four remaining populations in western Switzerland are small remnants of formerly large populations, whereas at most of the eastern sites, a tendency towards increasing population sizes was observed. The presented data will serve as a basis for further investigations into D. cristata as well as for future monitoring and conservation biology or genetics.